Testing the causes of middle Miocene Neotropical provinciality in South America

The Neotropics are home to exceptional levels of mammalian diversity, but few fossil-producing sites document the history and paleoenvironments represented by these faunas. Among these are two middle Miocene sites from the Andes of south-central Bolivia, Cerdas (~16 Ma) and Quebrada Honda (~13 Ma), which are relatively well-sampled and temporally well-constrained. Together, they span the end of the Middle Miocene Climactic Optimum (MMCO; Cerdas) and the interval directly following it (Quebrada Honda). Thus, they offer an opportunity to expand limited knowledge of Neotropical paleoenvironments and to investigate habitat changes that may have occurred in parallel with climate change during the MMCO and/or tectonic uplift that occurred during this interval. Paleopedology, ichnology, and an ecological diversity analysis (EDA) were used to reconstruct and compare the paleoenvironments of Cerdas and Quebrada Honda to one another and to several other sites (in the case of Quebrada Honda). Cerdas and Quebrada Honda are reconstructed to have sub-arid to humid climates with differing vegetative cover. The landscapes of Cerdas are interpreted as shrublands and open grassland-like environments, while the landscapes of Quebrada Honda are interpreted as moderately- to densely-vegetated wooded grasslands. The differing paleohabitats of Cerdas and Quebrada Honda primarily result from differencesin landscape stability and soil moisture and do not support suggestions of higher paleoelevations at Quebrada Honda relative to Cerdas at their times of deposition. An EDA using a worldwide modern comparative data set of temperate and tropical faunas was used to evaluate the habitats of five middle Cenozoic (Oligocene–Miocene) fossil faunas, including Quebrada Honda. The results indicate that modern faunas from other continents represent better analogues for ancient South American faunas than modern South American faunas. The inferred habitats of Quebrada Honda are compared to that of the contemporaneous (~13 Ma) and faunally distinct site of La Venta, Colombia. The paleoenvironments of these two localities are found to be drastically different, and the differences between the faunas are interpreted to reflect differing habitats. These findings are concordant with patterns of provinciality observed in ancient Neotropical faunas, and support the hypothesis that the provinciality is primarily a result of differing habitats.